Method of preventing the polymerization of unsaturated aldehyde

ABSTRACT

1. A STABILIZED SOLUTION CONSISTING ESSENTIALLY OF AN ALKANOL SOLUTION OF AN ALDEHYDE MONOMER SELECTED FROM THE GROUP CONSISTING OF ACROLEIN AND METHACROLEIN, SAID ALKANOL HAVING 1 TO 8 CARBON ATOMS AND FROM 0.001 TO 1% BY WEIGHT, BASED ON THE WEIGHT OF SAID MONOMER, OF A HYDROXYLAMINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF N-ALKYLHYDROXYLAMINE HAVING FROM 1 TO 8 CARBON ATOMS IN THE ALKYL GROUP, N,N-DIALKYLHYDROXYLAMINE HAVING FROM 1 TO 8 CARBON ATOMS IN EACH ALKYL GROUP AND N,N-DICYCLOHEXYLHYDROXYLAMINE.

United States Patent O US. Cl. 260-601 R 6 Claims ABSTRACT OF THE DISCLOSURE A method of preventing the polymerization of unsaturated aldehydes in alcohol solution, which comprises adding to the solution, as a polymerization inhibitor, a hydroxylamine of the formula:

( wherein R is selected from the group consisting of hydrogen, acyclic and cyclic hydrocarbon groups having 1 8 carbon atoms and R is selected from the group consis ting of acyclic and cyclic hydrocarbon groups having 1 8 carbon atoms),in an amount suflicient to inhibit polymerization. An unsaturated aldehyde/alcohol solution thus stabilized.

A BACKGROUND OF THE INVENTION 7 I i I Field of the In vention This invention relates to a methodof stabilizing unsaturated aldehydes,'i.e. to a method of preventing the polymerization of unsaturated aldehydes.

Description of the Prior Art- While unsaturated aldehydes such as acrolein or methacrolein are compounds which are valuable as starting materials in .thechemicalindustry, they are extremely unstable compounds which are liable to polymerize with e o For "example, such unsaturated aldehydes are usually present in.. an, alcohol solution, and areexposedto elevated temperatures, e.g. above 60 C., and particularly 80-150 C. or higher in the reaction, absorption, recovery, separation and purification operations in, for example, such processes as follows:

I (i) A process for separating unsaturated aldehydes (acrolein or'jmethacroleinj) from a gaseous mixture containing said-unsaturatedaldehyde obtained by the vapor phase oxidation ofan olefin (propylene or isobutylene),

which comprises absorbing the unsaturated aldehyde in a gaseous mixture with an alcohol solvent, and extracting the organicsolvent-from-theresulting solution by using water to thereby s'e 'narate'the unsaturated aldehyde asan' extraction residue phase and thereafter recovering and separating theunsaturated aldehyde from the'residue (ii) A process for production of an unsaturated acid In such processes the polymer separates out in the system to either become adhered to the walls of the reactor or clog the lines, etc., and hence becomes the cause of serious trouble in carrying out the operation. A loss of the unsaturated aldehyde monomer also, of course, results (unsaturated aldehyde monomer is often referred to merely as monomer). These are distinct commercial and economic disadvantages.

As inhibitors for preventing the polymerization of unsaturated aldehydes numerous compounds are generally used such as hydroquinone, metal compounds, thiocarbamic acid, etc. However, practically all of these compounds do not show any stabilizing effect, when the monomer is present in alcohol solution at elevated temperatures. Further, even in those cases where no separation of polymer is seen, it is observed that a decrease takes place in the amount of monomer. This loss of monomer is substantiated by analysis such as by gas chromatography. It is conceivable that the monomer loss is due to decomposition of the monomer, dimerization of the mono mer resulting from conjugate double bonds, the formation of a low polymer of an order that will not separate out, etc.

SUMMARY OF THE INVENTION One object of the present invention is to provide a method of effectively stabilizing unsaturated aldehydes, especially a method of preventing the polymerization and less of monomer in alcohol solution at elevated temperatures, by the discovery of an inhibitor which does not possess the hereinbefore noted short comings.

Other objects and advantages of the invention will become apparent from the following description.

As aresult of our research with a view to achieving the foregoing objects, we found that an alkylhydroxylamine was most useful as an inhibitor for unsaturated aldehydes.

Thusthese objects of the present invention can be achieved by adding an effective amount of a hydroxylamine of the formula:

(wherein R is selected from the group consisting of hydrogen, acyclic and cyclic hydrocarbon groups having 1-8 DETAILED DESCRIPTION OF THE INVENTION Examples of said hydroxylamine compounds used in the present invention include N-alkylhydroxylamines such as N-rnethylhydroxylamine, N-ethylhydroxylamine, N- propylhyd'roxylamine and N-butylhydroxylamine, N,N-

dihexylhydroxylamine, N,N-dialkylhydroxylamines such as N,N-dimethylhydroxylamine, N,N-diethylhydroxylamine, N,N di-n-propylhydroxylamine, N,N-diisopropylester by reactinga'n'unsaturated'aldehyde with hydrogen hydroxylamine, N,N-dibutylhydroxylamine, N,N-diamylhydroxylamine, N,N-dioctylhydroxylamine, N-methyl-N- ethylhydroxylamine, 'N-methyl-N-butylhydroxylamine, N- methyl-N-hexylhydroxylamine, N,N-diarylhydroxylamines such as N,N-diphenylhydroxylamine, N,N-dicycloalkylhydroxylamine such as N,N-dicyclohexylhydroxylamine and the like. Further, these hydroxylamines can be used in the form of their hydrate or salt wherein said salt is hydes) such as organic acids, e.g. acetic acid, acrylic acid, methacrylic acid, ketones such as acetone, are present in the alcohol solution containing the monomer, the stabilizing effect of the inhibitors of the invention is not derived from an organic acid such as hydrochloric, sul- 5 diminished.

furic acid or nitric acid, an organic acid such as oxalic While the amount of the inhibitor to be added is capaacid, malonic acid, citric acid, or an aliphatic acid conble of being 'widely varied depending upon the environtaining carbon atoms, p cially 1-4 carbon atoms, ment of the monomer, e.g., temperature conditions, such as formic acid, acetic acid, propionic acid, butyric amount of monomer in alcohol solution, the type of alacid, stearic acid and the like. Accordingly, these alkylcohol solution, the type of alcohol, or other conditions, hydroxylamine hydrates or salts are also included as init is at least 0.001% by weight, and usually 0.001 to hibitors in accordance with the present invention. 3% by weight, and preferably 0.01 to 1% by weight,

The preferred hydroxylamine is a N,N-dialkylhydroxylbased on the monomer. The amount added may, of course, amine having 1-6 carbon atoms, especially 1-4 carbon be increased, if desired. When the added amount is less atoms, in each alkyl group. 15 than 0.001% by weight, the effect of this invention cannot As unsaturated aldehydes, acrolein or methacrolein are be achived. On the other hand, when added amount is included in accordance with the invention. more than 3% by weight, there is no disadvantage on the Examples of alcohols to be used in the invention ineffect of stabilization, regardless of expense. Again, in clude aliphatic alcohols having a 1-8 carbon atoms, practicing the method of the invention, the known inspecifically alkanols such as methylalcohol, propylalcohol, hibitors of unsaturated monomers may be suitably used butylalcohol, isobutyl alcohol, hexylalcohol, n-octylalcoconjointly in standard, i.e., inhibiting amounts. hol or 2-ethylhexylalcohol. Further, while generally, the The following non-limitative examples are given to effect of this invention can be fully achieved regardless of more specifically illustrate the present invention. the weight ratio of the monomer to the alcohol, the preferred weight ratio of the monomer to the alcohol EXAMPLES AND CONTROLS is 0.03-z1.

That the inhibitor of the present invention shows a Th various i hibitors shown in Tables I and II were unique function or effect is substantiated by the fact that added to sample solutions containing the monomer p the marked stabilizing effect i has on the monomer (methacrolein or acrolein weight percent shown) shown in n t alcohol Solutwn, It has praetleally no effect on the 39 Tables I and II, after which the mixtures were charged into Stabilization of monomer in the abse e f So ve t, that an ordinary steel container. The mixtures were then heated it has practically no effect on the stabilization of monomer to a temperature of 100 C. and held at this tempearture in solvents other than alcohols, and that while the nufor 5 hours, at the end of which period the state of merous conventional inhibitors show practically no stapolymer separation was observed to determine if insoluble bilizing effect, the inhibitors of the invention not only polymer was formed (state of solution). When there was have an apparent stabilization effect but also have the no separation of polymer, the solution was added dropeffect of significantly preventing the loss of monomer. wise to n-hexane, and the presence or absence of polymer The inhibitors of the invention exhibit over a prolonged was confirmed by whether or not a precipitate was formed period of time a remarkable stabilizing effect unlike con- 40 (condition of dropping into n-hexane). Further, the mono ventional inhibitors even when monomer is exposed to mer content of the solution before its heating and after elevated temperatures, especially when monomer is presits heating was determined by gas chromatography, and ent in alcohol solution, not to mention the cases of being the decrease in monomer content was obtained by a comexposced to low temperature such as during storage of the parison of the two measurements (monomer decrease). monomer. And, open test effect of this invention can be The amount of inhibitor added is shown by weight percent achieved at elevated temperature, e.g. 100 C. In addition, based on the monomer. Further, the dash mark in this effect is not diminished even where the monomer is the table indicates where a measurement was not made, contacted with stainless steel or ordinary carbon steel. since the sample was solidified by heating, and measure- Again, even when water, or by-products (obtained by ment was deemed unnecessary. the vapor phase oxidation of olefins to unsaturated alde- The results obtained are shown in the following table.

TABLE I Weight Sample solution (composition, weight percent percent based on total composition) Condition based of dropping on the Water, State of into Monomer Ex. Inhibitor monomer Monomer Percent Alcohol Percent percent solution n-hexane increase 1 N,N-diethylhydroxylamine 0.1 Miathacrw 80 MethyL... 20 0 Colorless and No precipl- 0.9 0.1 e 15 as 0.1 40 9.2 0.1 50 2.5 0.1 5.8 0.1 0.5 0.1 3 3.5 0.1 3 Y 3.7 0.1 3 4.7 n 0.05l do 3 8.5 11--. do 0.1 Acrolein 3 2.9 12 N,N-dimethy1hydroxylamine..-.. 0.1 Miat hacro' .-do 3 3.6

9111. 13... N,N-diisopropylhydroxylamine 0.1 do 95 do......- 3 3.5 14 N,N-di-n-butylhydroxylamine 0.1 do 95 --.do-- 3 4.0 15 N,N-diethylhydroxylamine 0.1 do 80 ...d0 15 5.5

hydrochloride. 16... NJi-diethylhydroxylamine 0.1 do 80 ...do...... 15 6.0

S11 17 N,N-iitethylhydroxylamine 0.1 ...do 80 -.-d0....:; 15 6.5

8.08 8. 6. 1s N,N-di th 1h d 1 mi 80 ..d 20

assent? ..t o 8 me 0 It TABLE II Sample solution (composition, weight percent. Weight based on total composition) percent based Alcohol or Water, Condition of Conon the Perorgame Perper- State of dropping into Monomer trol Inhibitor monomer Monomer cent solvent cent cent solution n-hexane decrease 1- N,N-diethylhydroxylamine 0.1 Methacro- 100 0 Turbid. Large amount of 35.

1 lein. precipitation. 2 "do 0.1 Acrolein. 100 0 0 Solidified 3. N,N-dnsopropylhydroxylamme. 0.1 Mlethacro- 100 0 0 Polymer 28. 9

ein. formed. 4"-.. Hydroquinone 0.1 do 80 Methyl l 0 solidified.

a co 0 5 Sodium salt of N,N-dimethyldithi- 0.1 do 95 do 3 2 do ocarbamie acid. 6-.-" Copper acetate .1 .-do 95 ---..d0 3 2 do..- 7 Hydroqmnone 0.1 -do 95 do 3 2 do 8. p-t-Butyl catechol. 0.1 do 95 do 3 2 Turbid. Polymer separa- 86. 3

tion. 9... Phenothiazine 0.1 do 95 do 3 2 do -.do 36.5 10.. p-t-Butyl catechol. .t 0.1 do 95 Butyl 3 2 -.do do 24. 3

alcohols 11. N,N-diethylhydroxylam1ne 0. 1 do. 95 Benzene- 3 2 Trans ...do 21. 9

I parent. 12 N,N-di1sopropylhydroxy1amine...; 1 do 95 -do 3 2 do Large amount of 30. 3

precipitation. 13 do 0.1 do 80 do-. 20 0 do Polymer separa- 34. 7

on. 14- N,N-diethylhyd.roxylam.ine 0. 1 do 80 d0- 20 0 Turbid Large amount of 40. 1

precipitation. 0. 1 .do. 80 n-Hexane. 20 0 38. 3

0. 1 .do 80 Aeetone..-.. 20 0 35. 8

0. 1 ..do 80 Chloroform- 20 0 42.1 0. 1 o 80 Acetic acid" 20 0 32.5

0.1 do 80 Aceto- 20 0 29. 5

phenone. o. 1 do 80 Ethyl ether- 20 0 do do 35. 7

What is claimed is:

1. A stabilized solution consisting essentially of an alkanol solution of an aldehyde monomer selected from the group consisting of acrolein and methacrolein, said alkanol having 1 to 8 carbon atoms and from 0.001 to 1% by weight, based on the weight of said monomer, of a hydroxylamine compound selected from the group consisting of N-alkylhydroxylamine having from 1 to 8 carbon atoms in the alkyl group, N,N-dialkylhydroxylamine having from 1 to 8 carbon atoms in each alkyl group and N,N-dicyclohexylhydroxylamine.

2. The solution of Claim 1, wherein said solution is exposed to a temperature between 80 C. and 150 C.

3. The solution of Claim 1, wherein said hydroxylamine is present in said solution in the form of a hydrate or salt thereof, said salt being the salt of an acid selected from the group consisting of hydrochloric, sulfuric, nitric, oxalic, malonic, citric, and saturated aliphatic acids selected from the group consisting of formic acid, acetic acid, propionic acid and butyric acid.

4. The solution of Claim 1, wherein said hydroxylamine is a N,N-dialkylhydroxy1amine having from 1 to 6 carbon atoms in each alkyl group.

5. The solution of Claim 1, wherein the weight ratio of said monomer to said alcohol varies from 0.01:1 to :1,

UNITED STATES PATENTS 2,212,894 8/1940 Allen 260--67 3,408,422 10/1968 May 260837 R 2,939,882 6/1960 Mecorney 260601 R OTHER REFERENCES Schildknecht, C. E.: Vinyl and Related Polymers," Wiley, 1951, pp. 699-701.

LEON ZITVER, Primary Examiner D. B. SPRINGER, Assistant Examiner US. Cl. X.R. Z486 R 

1. A STABILIZED SOLUTION CONSISTING ESSENTIALLY OF AN ALKANOL SOLUTION OF AN ALDEHYDE MONOMER SELECTED FROM THE GROUP CONSISTING OF ACROLEIN AND METHACROLEIN, SAID ALKANOL HAVING 1 TO 8 CARBON ATOMS AND FROM 0.001 TO 1% BY WEIGHT, BASED ON THE WEIGHT OF SAID MONOMER, OF A HYDROXYLAMINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF N-ALKYLHYDROXYLAMINE HAVING FROM 1 TO 8 CARBON ATOMS IN THE ALKYL GROUP, N,N-DIALKYLHYDROXYLAMINE HAVING FROM 1 TO 8 CARBON ATOMS IN EACH ALKYL GROUP AND N,N-DICYCLOHEXYLHYDROXYLAMINE. 